1. Field
The present invention relates to tires for passenger vehicles and in particular to the beads of these tires.
2. Description of Related Art
Reducing the greenhouse gases emitted by vehicles is one of the major challenges facing today's vehicle manufacturers. The tire is a significant area in which progress can be made, via a reduction of the rolling resistance, because this has a direct impact on the fuel consumption of the vehicle. Appreciable progress has been made, as demonstrated for example by the great success enjoyed by the Energy® Saver tire recently brought to market by Michelin. The technology employed gives a saving of almost 0.2 l of fuel per 100 km in the mixed cycle, which equates to a reduction of almost 4 g of CO2 per km. This corresponds to approximately one tonne of CO2 that is not discharged into the atmosphere over the life of a vehicle.
Given the predicted increase in the cost of crude oil and the ever-growing consumer awareness of ecological issues, it is nonetheless necessary to continue work aimed at reducing the rolling resistance of tires.
The assembly formed by the bead and the radially inner part of the sidewall of a tire is one of the parts of the tire the structure of which has a very marked impact on the rolling resistance of the tire. It has many roles: it absorbs the tension of the carcass reinforcement and transfers the load to which the tire is subjected from the sidewall to the rim. It therefore guides the crown of the tire from the rim. Its impact on tire handling is considerable, particularly when the tire is heavily loaded. All these functions are usually obtained by combining a reinforcement (comprising the bead wire and the turn-back of the carcass reinforcement about this bead wire) and a “filler” made of rubber compound. The compromise between the stiffness that has to be achieved, particularly for guiding the crown, and the expected endurance generally leads the tire designer to having the carcass reinforcement follow a certain path and to using a filler that is bulky (tall and/or thick) and rigid. The downside of this geometry is significant hysteresis losses, notably in the filler. The stiffening effect of the filler is applied especially in the region remote from the bead and therefore requires a filler that is even bulkier and, therefore, results in ever greater hysteresis losses.